1. Field of the Invention
The present invention relates to an exhaust gas purifying system, a method for manufacturing the exhaust gas purifying system, and an exhaust gas purifying method using the exhaust gas purifying system.
2. Discussion of the Background
In exhaust gases discharged from an internal combustion engine such as a diesel engine, particulate matters (hereinafter, referred to as PMs) are contained, and in recent years, these PMs have raised serious problems as contaminants harmful to the environment and the human body. Moreover, exhaust gases also contain toxic gas components, such as CO (carbon monoxide), HC (hydrocarbon) or NOx (nitrogen oxides), and these toxic gas components have also raised serious problems as contaminants harmful to the environment and the human body.
Therefore, as the exhaust gas purifying apparatus that is coupled to an internal combustion engine so that PMs in exhaust gases are captured therein and toxic gas components contained in exhaust gases, such as CO, HC, NOx or the like, are purified, various exhaust gas purifying apparatuses have been proposed, each of which is composed of an exhaust gas treating body made from a porous ceramic material such as cordierite, silicon carbide, or the like, a metal casing used for housing the exhaust gas treating body therein, and a mat-shaped holding sealing material containing inorganic fibers, which is placed between the exhaust gas treating body and the metal casing.
In these exhaust gas purifying apparatuses, the holding sealing material is allowed to hold the exhaust gas treating body by the elasticity possessed by the inorganic fibers. Moreover, by filling a gap between the exhaust gas treating body and the metal casing with the holding sealing material, exhaust gases are prevented from leaking through a gap between the exhaust gas treating body and the metal casing.
As the method for manufacturing the exhaust gas purifying apparatus, a method has been known in which an exhaust gas treating body around which a holding sealing material is wound is stuffed (press-fitted) to the inside of a metal casing. As the metal casing, a metal casing, which has an inner diameter that is slightly shorter than the outer diameter (the combined length of the diameter of the exhaust gas treating body and the thickness of the holding sealing material) of the exhaust gas treating body around which the holding sealing material is wound, may be used.
In the present description, the exhaust gas treating body around which the holding sealing material has been wound is referred to also as “wound body”.
In an exhaust gas purifying apparatus produced by using the aforementioned method, the holding sealing material is brought into a compressed state inside the metal casing. Consequently, the holding sealing material is allowed to exert a restoring force (that is, holding strength for holding the exhaust gas treating body) for trying to return to its original shape by the elasticity possessed by inorganic fibers so that the exhaust gas treating body is held by the holding sealing material.
Moreover, an inlet pipe for introducing exhaust gases into the exhaust gas purifying apparatus is connected to one of the ends of the exhaust gas purifying apparatus, and an exhaust pipe for externally discharging the exhaust gases that have passed through the exhaust gas purifying apparatus is connected to the other end of the exhaust gas purifying apparatus so that an exhaust gas purifying system can be manufactured.
In the present description, in the exhaust gas purifying apparatus, the side of the end portion to which the inlet pipe is connected is referred to as “gas inlet side”, and the side of the end portion to which the exhaust pipe is connected is referred to as “gas outlet side”.
However, in the exhaust gas purifying system manufactured by using the conventional method, problems arise in that the side face of the holding sealing material wound around the peripheral portion of the exhaust gas treating body forming the exhaust gas purifying apparatus tends to be deformed, and upon allowing exhaust gases to flow thereto, the holding sealing material is damaged.
Referring to FIG. 1, the following description will discuss this problem in detail.
FIG. 1 is a cross-sectional view that schematically illustrates one example of a conventional exhaust gas purifying system. In FIG. 1, the stuffing direction is indicated by an arrow “Z”. In this manner, in the conventional exhaust gas purifying system, the stuffing direction and the flowing direction of exhaust gases are the same direction.
In a conventional exhaust gas purifying system 200 shown in FIG. 1, on the gas outlet side 212 of an exhaust gas purifying apparatus 210, the first side face 241 of a holding sealing material 240 is not made substantially in parallel with an outlet side end face 232 of an exhaust gas treating body 230 to cause a tilted state. Moreover, on the gas inlet side 211 of the exhaust gas purifying apparatus 210, the second side face 242 of the holding sealing material 240 is not made substantially in parallel with an inlet side end face 231 of the exhaust gas treating body 230 to cause a tilted state.
The reasons for this are presumably explained as follows: Upon stuffing the exhaust gas treating body 230 around which the holding sealing material 240 has been wound into a metal casing 220, a shearing force is exerted between a main face 245a (hereinafter, referred to also simply as a first main face) of the holding sealing material 240 that is made in contact with the exhaust gas treating body 230 and a main face 245b (hereinafter, referred to also simply as a second main face) of the holding sealing material 240 that is made in contact with the metal casing 220. The shearing force is exerted in a stuffing direction on the first main face 245a side of the holding sealing material 240, and is also exerted in a direction opposite to the stuffing direction on the second main face 245b side of the holding sealing material 240. It is considered that, as a result, the positions of the first main face 245a and the second main face 245b of the holding sealing material 240 are mutually displaced, with the result that the holding sealing material 240 is deformed.
Additionally, the expression “substantially in parallel with” indicates a state in which the end face (inlet side end face or outlet side end face) of the exhaust gas treating body is kept in parallel with the first side face or the second side face of the holding sealing material or a state in which, even when the first side face or the second side face of the holding sealing material is tilted relative to the end face of the exhaust gas treating body, the degree of the tilt can be virtually ignored.
As in the case of a conventional exhaust gas purifying system 200 shown in FIG. 1, in a state where, in an exhaust gas purifying apparatus 210, a first side face 241 and a second side face 242 of a holding sealing material 240 are tilted, upon allowing exhaust gases to flow thereto, an area at which the first side face 241 or the second side face 242 of the holding sealing material 240 is made in contact with the exhaust gases becomes greater. For this reason, the first side face 241 or the second side face 242 of the holding sealing material 240 tends to be easily subjected to wind erosion during the flowing of the exhaust gases. Moreover, the wind erosion generated on the first side face 241 or the second side face 242 of the holding sealing material 240 tends to progress to cause damages in the holding sealing material 240.
For this reason, in the case of a damage caused in the holding sealing material 240, it fails to sufficiently hold the exhaust gas treating body 230, as a result, a problem arises in that exhaust gases are leaked from a gap caused by the wind erosion, or in some cases, a problem arises in that the exhaust gas treating body 230 comes off.
In view of these problems, as an exhaust gas purifying apparatus forming an exhaust gas purifying system, for example, an exhaust gas purifying apparatus that uses a holding sealing material having a side face on which a slanting face is formed has been proposed, and a method for manufacturing such an exhaust gas purifying apparatus has also been proposed (JP-A 2007-092553).
The contents of JP-A 2007-092553 are incorporated herein by reference in their entirety.